Left Rear Fender Off

[55 Fargo]

Hi all, pulled left rear fender today, I had loosened the bolts a month or so back, only twisted off the front bottom bolt, the meatl holding the square nut was rotten and it twisted off, but I knew this going in.

I chased the remainder of the bolt holes. I have to weld or bond in a metal patch, no big deal. I was amazed to find some shiny black paint here and there under what was left of the welting.

But I do need to clean-up all the surface rust, then treat with acid, then it will get a couple of coats or rusty metal primer, then will be topcoated with enamel paint.

Sandblasting is not an option, and the wire brush attachment on grinder seems to polish up the rust, it also make sparks. I am not dropping my gas tank, so my filler neck is expeosed right now while I do this work.

Any suggestions, on what to use to strip and rust but this metal before acid prepping?

I may send the fender for sanblasting, of it's inner side, and mounting edges. I have my car off the road for the season now, and we just got snow on the ground a couple of days ago, so I am not driving it anywhere right now.

Just hunting for ideas, on the derusting processs..........Fred